1. Field of the Invention
The present invention relates to a light sensing panel and liquid crystal display apparatus having the light sensing panel. More particularly, the present invention relates to a light sensing panel that prevents lowering of aperture ratio, and a liquid crystal display apparatus having the light sensing panel.
2. Description of the Related Art
Generally, a light sensing sensor senses an external light to detect an entrance position of the external light. Willem den Boer disclosed a liquid crystal display apparatus having a plurality of the light sensing sensors arranged in a matrix shape to have a function of finger print identification or touch panel by a paper entitled “Active Matrix LCD with Integrated Optical Touch Screen” in 2003.
FIG. 1 is an equivalent circuit diagram of a conventional light sensing sensor formed in an array substrate. Particularly, FIG. 1 discloses the light sensing sensor formed in a unit pixel of a liquid crystal display panel.
Referring to FIG. 1, a liquid crystal display panel having a conventional light sensing sensor includes a plurality of gate lines GL, a plurality of data lines DL, a first switching device Q1 that is electrically connected to each of the gate lines and data lines DL, a liquid crystal capacitor CLC and a first storage capacitor CST1. Furthermore, the liquid crystal display apparatus includes a first power source line VL1 and a second power source line VL2, a second switching device TS1 generating currents in accordance with an external light, a second storage capacitor CST2 stores electric charges provided from the second switching device TS1, a third switching device TS2 that outputs the electric charges stored in the second storage capacitor CST2, and a readout line ROL. The second switching device TS1, the second storage capacitor CST2 and the third switching device TS2 operate as a light sensing sensor.
Hereinafter, an operation of the light sensing sensor will be explained.
When the second switching device receives an external light, a negative voltage is applied to the first power source line VL1, and a positive voltage is applied to the second power source line VL2 that is electrically connected to a drain electrode of the second switching device TS1, so that the second switching device TS1 is turned off. Then, the second switching device TS1 that receives the external light generates more photocurrent than the third switching device TS2 that does not receive the external light.
The photocurrent charges the second storage capacitor CST2 with electricity when the third switching device TS2 is turned off. The second storage capacitor CST2 maintains electric charges until the third switching device TS2 is turned on.
When a gate signal of high level is applied to a next gate line GQ+1 that is electrically connected to the third switching device TS2, electric charges stored in the second storage capacitor CST2 are applied to a readout circuit section (not shown) via the third switching device TS2 and a readout line ROL.
As described above, the light sensing sensor formed on the array substrate detects a light.
However, a size of a region in which the light sensing sensor is disposed is insufficient. Therefore, a design for the array substrate may be limited.
When the light sensing sensor is employed by the array substrate of a transmissive type or transflective liquid crystal display apparatus, an aperture ratio is lowered. Additionally, the light sensing sensor has two transistors and one capacitor, that is, the light sensing sensor has tree devices. Therefore, possibility of defects may increase. Furthermore, possibility of interference between the devices may also increase.